Electron discharge tube having improved cooling means therefor



28, 6 c. A. E. BEURTHERET 3,366,350

' ELECTRON DISCHARGE TUBE HAVING IMPROVED COOLING MEANS THEREFOR 'Filed May 13, 1963 4 Sheets-Sheet 1 FIG..I

(bar/95A 40h onseEmi/e fled/Me re1 IN VENTOR.

Feb. 28, 1967 I c. A. E. BEURTHERET 3,306,350

ELECTRON DISCHARGE TUBE HAVING IMPROVED COOLING MEANS THEREFOR Filed May 13, 1963 Y 4 Sheets-$heet z FIG.3I

FIG.5

Char/es A 40/70/6615??? /'/e Bear/he ref INVENTOR.

BY PJE LATJM Arr 0 Feb. 28, 1967 c. A. E. BEURTHERET 3,306,350

ELECTRON DISCHARGE TUBE HAVING IMPROVED COOLING MEANS THEREFOR Filed May 13, 1963 4 Sheets-Sheet 5 (/25: r/es A nhonjefmfle fieuff/veref INVENTOR.

WAWDM A TTO/F/VEY 23, 1967 c. A. E. BEURTHERET 3,306,350

ELECTRON DISCHARGE TUBE HAVING IMPROVED COOLING MEANS THEREFOR Filed May 13, 1963 4 Sheets-Sheet 4.

IN VEN TOR.

ATTOE/VF/ United States Patent 3,306,350 ELECTRON DISCHARGE TUBE HAVING IM- PROVED COOLING MEANS THEREFOR Charles Alphonse Emile Beurtheret, Saint-Germain-en- Laye, France, assignor to Compagnie Francaise Thomson Houston-Hotchkiss Brandt, a corporation of France Filed May 13, 1963, Ser. No. 279,305 Claims priority, application France, May 22, 1962, 898,347, Patent 1,346,268 11 Claims. (Cl. 165-405) This invention relates to cooling arrangements for electron discharge tubes. In high-power electronic tubes considerable heat is generated in the operation of the tube by the intense bombardment of the anode or collector electrode surface of the tube with electrons from the cathode or emitter electrode thereof. The dissipation of this heat at the rate required for a successful continuous operation of the tube poses serious problems and in the past has frequently set a limit to the maximum power rating with which the tubes could be built.

The invention is concerned with the application to electron tubes of cooling systems of the evaporation cooling type, in which a vaporizable fluid, usually water, is used as the medium for removing the heat from the heated surface, by way of a heat exchange wall or partition surrounding said surface, the outer surface of which wall is mintained in contact primarily with the boiling liquid. The advantages of evaporation cooling as contrasted with cooling by means vof a fluid provided in a single phase, liquid or vapour, are well-known, and the method has been used for many years in various fields of engineering, including electron discharge tubes.

It would clearly be advantageous if the evaporating fluid surrounding the anode structure in an electron tube could be maintained at substantial superatmospheric pressure, since this would permit higher heat dissipating rates due, inter alia, to the increase in the temperature difference between the vapour generated on contact with the heat dissipating surface, and the secondary cooling medium used, as well as other causes. However, prior attempts to develop evaporation coolers for electron tubes that would operate successfully at substantial over-pressure say higher than one atmosphere gauge, have been unsuccessful, to the best of applicants knowledge, and such over-pressures, when used at all, have been limited to a fraction of one atmosphere above normal atmospheric pressure. The general reason for this has been that it was found difficult or impossible to maintain a stable and limited temperature gradient, without any tendency to the formation of hot spots at which the temperature would locally rise to extremely high values leading to a destruction of the metal surfaces, at higher pressures.

The applicant has been engaged for many years in the study of evaporation cooling systems and has developed such systems in which hot spot formation is positively avoided by the maintenance of stable temperature gradients over the heat dissipating surfaces. This result has been attained by certain specific teachings as to the geometry of heat dissipating formations, such as ribs, fins and grooves, provided on the surface of the heat exchange wall in contact with the evaporable fluid, whereby stable non-isothermal temperature conditions were created over the surface. These prior teachings have been disclosed, inter alia, in the following prior patents and applications of the applicants Patent Nos. 2,935,305, 2,882,449 and co-pending application No. 260,245 filed February 21, 1963, now Patent 3,235,004.

The present invention has as its chief object the provision of evaporation cooling means for high-power electron tubes which will be operable at greatly higher pres- 3,396,350 Patented Feb. 28, 1967 sures than any heretofore available, with attendant benefitsas to increase in the cooling rates attainable and hence the maximum permissible power ratings of electron tubes that can be built. An object is to provide an evaporation cooler for an electron tube that can be safely and reliably operated for indefinitely long periods of time at pressures of more than three, and preferably more than five atmospheres gauge. Further objects are to provide high-power electron tubes, including field control 'tubes, klystron, travelling-wave tubes and other velocity modulation tubes, having higher cooling rates and correspondingly higher performance characteristics, than tubes now available. Other objects will appear.

The invention lies essentially in applying certain of the teachings earlier disclosed by the applicant, and more specifically the teachings of the co-pending Patent 3,235,- 004 to the provision of high-pressure evaporation cooling means for electron tubes.

In the co-pending application just mentioned, an evaporation cooling system was disclosed in which the heat exchange wall externally provided, on its surface in contact with the evaporable fluid, with heat dissipating formations in the nature of grooves and fins so dimensioned as to satisfy the relations b=m\/ac and d b/3, wherein b is the depth of the groovesadjacent ribs, d the width of said grooves, a the average transverse thickness of the ribs, c the heat conductivity factor of the material from which the wall is made, and m a numerical factor. When b, d and a are expressed in centimetres and c in 'watts per centimetre per degree C, m is of the order of unity. As explained in the co-pending application, thus proportioning the heat dissipating formations of an evaporation cooler, represents a radical departure from the shapes and sizes of the ribs or fins earlier used, and results in the establishment of extremely stable temperature gradients encompassing the so-called critical temperature range which in earlier evaporation coolers could not be exceeded without bringing about sharp and irreversible temperature rises, to 1000 C. or more, which would immediately lead to the destruction of the metal. With the improved geometry, the operating temperatures and hence the cooling rates of evaporation coolers could be substantially increased without accompanying danger of hot spot formation.

' It has been found that the application of the above teachings in regard to the shape and dimensions of the heat dissipating formations on the heat exchange wall of an evaporation cooler provides a means of safely and stably operating the cooling devices of electron tubes under pressures higher than atmospheric, e.g. 5 atmospheres and more. This is in excess of pressures heretofore found possible, thus bringing great practical advantages and correspondingly increasing the performance characteristics of the tubes as well. as the power ratings at which it is feasible to construct them.

One major reason why pressurizing the evaporation cooler increases the heat dissipation rate is that the increase in pressure reduces the total volume of the vapour phase and also, though to a smaller extent, the average diameter of the individual vapour bubbles formed. Since the dimensions of the heat dissipating ribs and the intervening grooves on the heat exchange wall in contact with the vapour should both be closely related to the meandimensions of the vapour bubbles, it is evident that increasing the pressure should make it possible to reduce proportionately the over-all dimensions and diameter of the anode while maintaining a given contact area between it and the fluid, thereby increasing the specific heat dissipation rate per unit over-all area. However, when it was attempted to apply high pressures to factory for proper operation of the exchanger.

evaporation coolers constructed in accordance with the earlier art, a stable temperature gradient could no longer be obtained over the heat dissipating surface, hot spot formation could no longer be avoided, and failure of the anode surface ensued.

On the other hand, if the heat dissipating formations are provided in accordance with the geometrical relations disclosed in the co pending application, it becomes possible to vary the dimensions of said formations without effecting the stable temperature gradients and hence without any danger of hot spot formation, provided the two above-specified conditions are satisfied. Thus, for a given superatmospheric pressure in the evaporation cooler, it is possible to provide a maximum number of dissipating elements by selecting the width of the grooves at the minimum value consistent with a ready generation of the-vapour under the selected high pressure. Further, even for a material of given heat conductivity (about 3.7 for copper), it is always possible to select the width of the dissipating ribs at a value that will be consistent with the relations given. Thus the choice of the material provides an additional parameter whereby it will be possible, for example, to avoid having to provide rib widths of inadequate thermal inertia and mechanical strength.

For example, using an over-pressure of five atmospheres in the pressure enclosure of the evaporation cooler and water as the cooling fluid, it is found that grooves of the order of about one millimetre in width are satis- If copper is selected as the material from which the heat exchanger wall surrounding the anode is made, and using a groove width of d=2 mm., it is found that ribs only 2 mm.

vthick (dimension (1) are consistent with the specified mathematical relations and a groove depth of 11:12 mm. is permissible. Using these or an equivalent set of dimensions, there is obtained a resulting heat exchange area of extraordinarily large value, for a given overall size. The resulting electron tube evaporation cooler can be successfully operated at pressures of five atmospheres gauge and higher, and exhibits a cooling rate unattained in the prior art.

The present invention is directed to this particular application of the aforementioned earlier teachings of the applicant. The invention will now be described with reference to certain illustrative embodiments selected by way of example but not of limitation and illustrated in the accompanying drawings, wherein:

FIG. 1 is an elevational view of a high power field control triode provided with anode cooling means according to a first embodiment of the invention, in which the pressure enclosure or boiler is sealed and air is used as a secondary cooling agent; the right side of the drawing is, generally, an axial section while the left side is an outer view with parts broken away;

FIG. 2 is a partial plan view in section on the line IIII of FIG. 1;

FIG. 3 is a simplified view of a triode provided with cooling means according to another embodiment, in which a liquid is used. as a secondary cooling liquid, the showing being generally the same as in FIG. 1;

FIG. 4 is a simplified view, with parts broken away and shown in axial section, of a tube provided with cooling means according to another modification of the invention, wherein the evaporable fluid is continuous-1y circulated through the pressure enclosure;

FIG. 5 is a small-scale flow diagram illustrating the external circulating and cooling circuit for the evaporable fiuid, applicable to the form of embodiment of FIG. 4;

FIG. 6 is a view generally similar to FIG. 4, illustrating a further modification of an evaporation cooler for an evaporation cooler for an electron tube according to the invention; and

FIG. 7 is a flow diagram similar to FIG. 5 but relating to the modification shown in FIG. 6.

In the embodiment shown in FIGS. 1 and. 2, the invention is applied to the cooling of a V.H.F. triode generally designated 1, which may per se be conventional so that the internal details of it have not been shown. Suffice it to say that the triode includes a generally cylindrical grid structure G surrounding a cathode C and surrounded in turn by the wall of the cylindrical lower end cavity of an anode member 2 which extends upward to define an anodic enclosure above the electrodes. The anode member 2 constitutes at its cylindrical outer surface 5 a heat exchange wall made of copper or the like from which extend, in a radially outward direction, heat dissipating elements in the nature of ribs or fins 7 separated by grooves. In accordance with the aforementioned co-pending application, the ribs and intervening grooves are dimensioned in accordance with the relation b=m /ac wherein b is the depth of a groove, a the average thickness of a rib, c the thermal conductivity of the material from which the wall is made, and In is a numerical factor of the order of unity when a and b are expressed in centimetres and c in watts per cm. per degree C.; further the average width d of the grooves should be less than one third of the depth b, and preferably not less than one twelfth thereof.

It will be observed that in the operation of the tube, electron bombardment from the cathode C heats the anode surface constituted by the inner cylindrical surface in the lower cavity of member 2; this anode surface, extending between the end points designated 3a and 4a in FIG. 1, forms the heat input surface of the evaporation cooler. The heat output surface of the latter is the cylindrical outer surface of wall 2, provided with the heat dissipating fins, and extending approximately between the end points designated 3 and 4. In accordance with a desirable arrangement, disclosed and claimed. per se in the applicants co-pending patent application now Patent 3,235,004 the heat output surface 34 of the cooler is axially displaced from, and is herein longer than, the heat input surface I'm-4a, the advantage of this arrangement being described fully in the application just referred to.

In View of'the high pressure operation of the cooler system of the invention, e.g. at a pressure of about five atmospheres, it has been possible it impart relatively very small dimensions to the grooves between the heat dissipating formations 6 and to the said formations, so that the latter herein assume the forms of relatively thin fins. Thus in one satisfactory practical construction of the device shown, the fins 6 were about 2 mm. thick, the grooves between them 2 mm. Wide, and their average depth 10 mm.

The cylindrical member 2 is formed with a radial base flange 9, to the bottom of which is secured a connector assembly indicated herein in general outline only since its internal construction is immaterial to the present invention. The connector assembly may include, as shown, stepped connector elements connected internally to respective electrodes of the electron tube 1. An outer shell 10 of cylindrical form is secured by means of an inturned flange at its lower end around the flange 9 of the member 2 and extends upwards therefrom. The upper end of shell 10 is sealed by means of an end cover member 11 having its outer margin welded to the inner surface of the top of shell 10, and preferably having the curved profile shown. The end cover 11 is shown as provided with two fusible safety elements therein. A central fusible disk 14 is replaceably secured in the central region of cover 11 by means of screws 16 between flanges 15; the fusing of disk 14 under abnormal heating conditions serves to vent the inner pressure cavity to atmosphere. A second fuse element 17 inserted in a side part of the end cover 11 is rigidly connected through a Wire 18 anchored therein and a suitably guided rod 19 a cut-off switch 20 so that the fusing of element 17 will act to open the switch 20 and cut off the supply of power to the electron tube 1. Fuse 17 also is readily replaceable.

The cavity, defined within shell and bounded at its upper end by the cover plate 11 forms a pressure enclosure or boiler constructed to withstand the selected operating pressures with a suitable safety margin. Conventional secondary cooling means are provided to remove heat frorn'the outer wall of the pressure enclosure and are shown as comprising vertical fins 21 projecting from the outer cylindrical surface of the shell 10, and positioned in a suitable air draft. It is suflicient that the air radiator thus provided be dimensioned to dissipate the average power developed by the tube, rather than the maximum or peak power the tube may occasionally develop for limited periods of time, say some seconds. An outer conduit 22 surrounding the fins 21 limits the cooling air-stream from a fan, not shown, said airstream being indicated by the arrows F in FIG. 1.

Means are preferably further provided for improving the heat transfer between the shell 10 and the liquid and vapour phases of the boiling fluid within the enclosure, and said means comprise fins 12 projecting from the inner surface of shell 10 above the separating wall member 2 so as to be in contact with the vapour phase of the boiling fluid in operation as will presently be described. Further, a cylindrical guide baflle wall 13 is preferably provided around the wall member 2 and spaced a substantial radial distance from the outer ends of-the fins 6 thermosyphon effect in the lower part of the pressure chamber.

In operation, the vapour forming the liquid, e.g. water, contained in the lower part of the pressure enclosure, in the area of contact with the anode structure 2, condensespartly where it touches the body of fluid in the liquid phase, as indicated at 8, and is set into rapid circulatory motion by thermosyphon eflect around the cylindrical baffle 13. This circulation considerably activates the heat exchange between the liquid and the lower part 10a of the shell 10. The vapour escaping from the liquid 8 into the free space above the free level 23 of the body of liquid, is compressed in said space and condenses over the upper parts 10b of the shell 10 including the surfaces of the fins 12. For a given power developed in the operation of the tube 1, there obtains within the body 8 an equilibrium condition as to the pressure and temperature therein, depending among other factors on the secondary air cooling rate between the radiating fins 21 and cooling air draft F.

In the construction disclosed, the pressure within the enclosure increases with the power dissipated by the tube, and hence the heat exchange rate from the heat dissipa-ting anode formations 7 also increases, i.e. the efficiency rises, as the power dissipation of the tube increases. This is chiefiy due to the fact that the high pressure of the compressed body of vapour in the upper part of the enclosure ensures stable boiling in the liquid, in spite of the relatively very narrow width of the grooves between the fins 7.

As to the function of the two safety fuse devices 14 and 17, it will be understood that the central fuse 14 provides mechanical protection against the danger of blowout of the boiler shell, while the fuse 17 provides an electrical safeguard against anode destruction by cutting off the power supply of the tube in case of overheating. Easy replacement of each fuse will recondition the sys tem for operation in either case.

In the form of embodiment illustrated in FIG. 3, the anode member 2a of an electron tube In is shown in broken-line outline, and is of upwardly tapered frustoconical shape instead of being cylindrical. The heat dissipating elementsor fins 7a provided on the outer surface of themember 2a are of corresponding configuration, and it will be understood that said elements 7a as well as the intervening groovesare again dimensioned in accordance with the teachings of the aforementioned co-pending application. The boiler shell 10a defining the pressure enclosure is herein provided in the form of an integral domed cylindrical member having a base aperture fitted around the base flange of the tube by way of seating ring 42 and a compressible seal ring 43 providing a detachable pressure tight seal. In this embodiment the secondary cooilng system uses water under pressure, and comprises a water coil 24 having an outer layer of turns surrounding the outer surface of the shell 10d and a plurality of inner layers of coils extending through a major region of the inner space of the pressure cavity, both in the upper (vapour) part of it and in the lower (liquid-phase) part around the anode member 2a, and both within and outside the thermosyphon baflie 13a. The outer turns of the coil are secured to the outer shell surface as by welding at 25. The coil 24 is supplied with water from a suitable pressure source through an inlet connection at the top of the outer layer of turns, and the water is discharged from the coil by way of an outlet connected to the upper end of the innermost layer of turns. A purging or drain cock 31 is connected to the lowermost outer turn. The coil 24 is led into and out of the pressure enclosure through apertures in the base and in the upper end of shell 10d.

Since heat exchange between fluids through the walls of a coil is generally more eflicient in the liquid rather than in the gaseous phase, the shell 10d is preferably filled with water up to a free level 2311 which is higher than in the preceding embodiment, so as to leave at the top of the enclosure only a relatively small free space as required for proper circulation of the emulsion formed by the liquid and vapour phases of the primary cooling fluid. The circulation is again due to thermosyphon effect and is enhanced by the provision of the cylindrical baflle 13a. The safety means shown in this instance include a central safety valve 26 biassed by a calibrated spring 27 against a seal ring 30, and a pressure-responsive relay device 28 connected through a rod 29 of insulating material to actuate a power cut-off switch 20a.

An evaporation cooler of the type shown in FIG. 3 will usually employ ordinary city water as the secondary cooling medium circulated through the coil 24. Means are desirably provided for regulating the flow rate of the secondary cooling water through coil 24 in accordance with the variations in mean power developed by the electron tube to be dissipated as heat. Such regulation can conveniently be provided through the use of a thermostat-controlled valve 32 interposed at the outlet from coil 24 and acting to increase the flow rate with increasing temperature sensed at the coil outlet. This arrangement has the advantage of limiting the flow rate of the water from the mains to the value strictly :required at any time. It will be noted further that in this embodiment the cooling system provides a source of hot water at substantially constant temperature as a by-product of the cooling process and at no extra cost, which water can conveniently be used for space-heating and similar purposes.

The further cooling system illustrated in FIGS. 4 and 5 shows an example of a pressure evaporation cooling system for an electron tube according to the invention in which the evaporable fluid is continuously circulated through the pressure enclosure. The boiler shell 10e in this case, which may be generally similar in shape to the shell 10d in FIG. 3, has a pair of inlet and outlet tubes 33 and 34 connecting with its upper section, for connection with a liquid circulating system not shown, the flow directions being indicated by the arrows F2 and F3. The evaporable cooling medium is advantageously distilled water. The shell like is internally provided with means for enhancing the uniform mingling of the liquid injected through inlet 33 with the liquidvapour emulsion of the boiling fluid within the enclosure, and said means are shown as comprising a diffuser 35 positioned across the inlet path of the injected liquid,

and a tubular bafile wall 36 depending from the top of the shell and serving to lengthen the path of the liquid fiow through the enclosure in that it constrains the liquid to flow from top of the enclosure within the batfie wall 36, through the diffuser mesh 35, down around the anode structure 20, herein shown in outline as a frustoconical structure of somewhat greater vertical extent than in the preceding embodiments, down and around the lower end of the baffie wall 36 and up into the outlet 34 outside said baffle wall. It will be noted that with the arrangement shown the inlet 33 for fresh cooling liquid delivers into the area of the enclosure which is richest in vapour concentration. This arrangement accelerates the onset of condensation of the vapour and the condensation then proceeds in the vicinity of the anode structure 20, continuing as far as the annular space 37 below the outlet 34. Just below this outlet a hole 44 is preferably formed through the baflle 36 to prevent formation of air pockets in the top of the boiler enclosure.

The safety features provided in this embodiment include by way of example a central spring-biassed safety valve 26a similar to that shown in FIG. 3. Instead of or in addition to this a safety valve can be installed in the flow circuit of the primary cooling liquid, and arranged if desired to protect more than one evaporation cooling system similar to the one described and forming part of a multi-tube electronic circuit installation. Safety switch means similar to those disclosed with reference to FIG. 1 or FIG. 3 may also be provided if desired.

In FIG. 5 the cooling system of FIG. 4 is schematically shown as connected in its secondary cooling circuit, which includes a pump 45 and a heat exchanger 46 supplied with any suitable secondary cooling agent, such as cool air from a fan 47. The system is shown as including an overhead pressurizing tank 48 serving to maintain a substantially constant over-pressure within the circuit while allowing for thermal expansion of the liquid and volume variations in the steam within the boiler. The pressurizer tank is a sealed vessel connected at its base with an upper point of the fiow circuit, to provide a variable space for compressed vapour in the top of the tank. The pump 45 should have a delivery high enough to ensure that the temperature of the liquid within the pressure enclosure will at all times be limited to a range which will still permit condensation of the vapour in the liquid, and will of course depend among other factors on the cooling capacity of exchanger 46. However, it can be shown that a relatively low power pump 45 can be used in view of the high pressure in the cooling circuit and the negligibly low value of the pressure loss in the boiler.

In the further embodiment shown in FIGS. 6 and 7, the arrangement is such that the vapour of the primary cooling fluid generated in contact with the heat dissipating formations on the anode structure are condensed outside the actual boiler or pressure enclosure, rather than within the enclosure as in the preceding embodiments. From the simplified general view of FIG. 6 it will be seen that the enclosure shell 10 is provided centrally of its upper wall with an outlet valve 38 biassed to closed position by a spring 40 calibrated for the nominal pressure to be maintained within the pressure boiler. Around the valve 38 the top of the shell 10f connects with a discharge conduit 39. The primary cooling liquid, e.g. water, is introduced into the base of the enclosure through an inlet 41 connecting with the side of the shell 10 The delivery rate of the liquid should be higher than the maximum rate of vaporization at the highest power dissipated at the anode of the electron tube 1d in steady-state operation. Excess unvaporized liquid from the pressure enclosure is carried out with the vapour into the outlet pipe 39. The pressure in the outlet pipe 39 can be quite low, e.g. close to ordinary atmospheric.

If desired, the enclosure 10] may be internally provided with steam deflector means, not shown, for reducing the amount of liquid entrained out of the enclosure with the vapour discharged through valve 38. Such a deflector means may be similar to that described in applicants application No. 30,720 filed May 19, 1959. As also described in that patent, the liquid delivered into the enclosure through inlet 41 may have served to cool other heat dissipating elements, of relatively low dissipating capacity, which may, or may not, form part of the electron tube.

It will be noted that in the embodiment of FIG. 6 mechanical protection against explosion of the pressure enclosure 10 is inherently provided by the vapour discharge valve 38 present in this construction. In addition, electrical protection can be provided in the form of safety fuse switch means similar to those shown at 17-20 in FIG. 1, or 28 in FIG. 3.

As shown in the diagrammatic view of FIG. 7, the cooling circuit for the system of FIG. 6 may include a condenser-exchanger 50 cooled by an airstream produced by a fan 51, and a pump 49 connected in series between the outlet pipe 39 and inlet 41. The pump 49 is of volume type, e.g. a gear pump or other positive-displacement pump, capable of imposing a prescribed volume flow rate for the liquid supplied to the evaporation cooler.

The primary cooling liquid used in the improved pressurized evaporation cooling systems of the invention can conveniently be distilled water, which has satisfactory thermal properties for the present purpose so that temperatures of C. can be maintained with pressures of about five atmospheres in the system. Damage due to freezing of the water in the system during idle periods can be prevented by the addition of an antifreeze agent, such as 5% ethylglycol. The applicant has found that the addition of such a low proportion of antifreeze agent is satisfactory in that it prevents expansion of the ice rather than actually preventing freezing. However, cooling fluids other than water can be used in the pressurized evaporation cooling systems of the invention, including any of the organic fluorinated compounds widely used for similar purposes.

It will be apparent that various modifications may be introduced into the exemplary embodiments disclosed herein without exceeding the scope of the invention. Depending on the capacity required for the pressurized boiler enclosures of the invention in view of the power rating of the electron tubes to which they are applied, the selected operating characteristics in regard to pressure and temperature, and other factors, the strucural features may be modified. Thus it will be noted that in the embodiment of FIGS. 1 and 2, the enclosure 10 is permanently welded to the flange 9 of the anode structure so that it is not adapted for disassembly by the user. In the FIG. 3 embodiment on the other hand, the pressure enclosure or boiler 10d is of a construction such that it can readily be dismantled if desired for maintenance purposes, owing to the autoclave-type seal assembly provided by the dual flange mounting of the shell 10d around the seating ring 42 and seal ring 43. Such a construction might of course be used in connection with the other embodiments shown should this be desired.

It will be apparent that the invention has made it possible to provide for the first time pressurized evaporation cooling systems for electron tubes, due to the improved geometry of the heat dissipating formations at the outer surface of the heat exchange wall in contact with said medium, as disclosed in the aforementioned co-pending application. This combination of concepts has made it feasible for the first time to apply substantial over-pressures, of the order of 5 atmospheres and more, to the evaporation coolers of electron discharge tubes, thereby greatly increasing the maximum permissible power ratings with which such tubes can be constructed. Space requirements are simultaneously reduced. The resulting over-all cooling systems are compact, economical and convenient to operate and maintain.

I claim:

1. The combination with an electron discharge tube including an electrode adapted to be heated through electron bombardment, of a cooling arrangement for said electrode comprising a heat exchange wall made of heat conductive material surrounding said electrode, a pressure resistant shell surrounding said heat exchange wall in spaced relation therewith and defining a pressure enclosure therearound, a body of vaporizable fluid in said enclosure, heat dissipating formations provided on the outer surface of said heat exchange wall projecting into said fluid to vaporize same and dimensioned in accordance with the relations b=m /ac and d b/3, wherein b is the depth of the grooves, d the width thereof, a the average thickness of the ribs, the heat conductivity of said wall material and m a numerical factor, said heatdissipating formations further having a depth b less than 12 mm., so as to establish stable temperature gradients over said surfaces, and means for maintaining a pre scribed pressure on said fluid within the enclosure of at least three atmospheres above normal atmospheric pressure.

2. The combination claimed in claim 1, wherein said prescribed pressure is at least about five atmospheres above normal atmospheric.

3. The combination claimed in claim 1, including a cylindrical wall within said enclosure surrounding said heat exchange wall in spaced relation therewith.

4. The combination with an electron discharge tube including an electrode adapted to be heated through electron bombardment, of a cooling arrangement comprising a heat exchange wall closely surrounding said electrode, a pressure-resistant shell surrounding said wall in spaced relation therewith to define a pressure enclosure therearound, a body of vaporizable fluid sealed within said enclosure, heat dissipating formations on the outer surface of said wall projecting into the fluid to vaporize same and dimensioned in accordance with the relations b=m /ac and d b/3, wherein b is the depth of the grooves, d the width thereof, a the average thickness of the ribs, c the heat conductivity of said wall material and m a numerical factor, said heat-dissipating formations further having a depth b less than 12 mm., so as to establish stable temperature gradients over said surfaces, means for maintaining a prescribed pressure on the fluid in said enclosure of at least three atmospheres above normal atmospheric, and flow means for passing a secondary cooling fluid in heat exchange relation with the first fluid in said enclosure.

5. The combination claimed in claim 4, wherein said flow means comprise means for creating a stream of said secondary cooling fluid around the outer surface of said shell.

6. The combination claimed in claim 4, wherein said flow means comprise coil means extending through said shell into said enclosure and means connected to said coil means outside the shell for circulating said secondary cooling fluid through the coil means.

7. The combination claimed in claim 4, including means responsive to the temperature of said secondary cooling fluid at its discharge from heat exchange relation with said first fluid, and valve means connected to said flow means for control by said temperature responsive means to vary the flow rate of said secondary fluid so as to maintain said temperature within a prescribed range.

8. The combination with an electron discharge tube including an electrode adapted to be heated through electron bombardment, of a cooling arrangement comprising a heat exchange wall closely surrounding said electrode, a pressure-resistant shell surrounding said wall in spaced relation therewith to define a pressure enclosure therearound, inlet and outlet means for a vaporizable fluid connected to spaced points of said enclosure, heat dissipating formations on the outer surface of said Wall projecting into said fluid to vaporize same and dimensioned in accordance with the relations b=m /Zi6 and d b/3. wherein b is the depth of the grooves, d the width thereof, a the average thickness of the ribs, c the heat conductivity of said wall material and m a numerical factor, said heat-dissipating formations further having a depth b less than 12 mm., so as to establish sta-ble temperature gradients over said surface, flow means connected with said inlet and outlet means externally of said shell, and means for maintaining a prescribed pressure on the fluid in said enclosure of at least three atmospheres above normal atmospheric.

9. The combination claimed in claim 8, wherein said means for maintaining the prescribed pressure include a pressurizing vessel connected to said flow means externally of said shell.

10. The combination claimed in claim 9, including bafflle means between said inlet and outlet for lengthening the path of the liquid through the enclosure.

11. The combination with an electron discharge tube including an electrode adapted to be heated through electron bombardment of a cooling arrangement comprising a heat exchange wall closely surrounding said electrode, a pressure-resistant shell surrounding said Wall in spaced relation therewith to define a pressure enclosure therearound, an inlet for vaporizable liquid connected to a bottom point of said shell, an outlet for vapour of said liquid connector to an upper point of said shell, heat dissipating formations on the outer surface of said wall projecting into said liquid to vaporize same wherein said heat dissipating formations comprise ribs and intervening grooves dimensioned in accordance with the relations pressure of at least three atmospheres above normal atmospheric.

References Cited by the Examiner UNITED STATES PATENTS 2,166,685 7/1939 Henderson et al. 315l18 2,882,449 4/ 1959 Beutheret -106 X 2,977,498 3/1961 Bychinsky 3l310 X 3,235,004 2/1966 Beurtheret 165-l05 X FOREIGN PATENTS 809,170 2/1959 Great Britain. 873,933 8/1961 Great Britain.

ROBERT A. OLEARY, Primary Examiner. A. W. DAVIS, Assistant Examiner. 

1. THE COMBINATION WITH AN ELECTRON DISCHARGE TUBE INCLUDING AN ELECTRODE ADAPTED TO BE HEATED THROUGH ELECTRON BOMBARDMENT, OF A COOLING ARRANGEMENT FOR SAID ELECTRODE COMPRISING A HEAT EXCHANGE WALL MADE OF HEAT CONDUCTIVE MATERIAL SURROUNDING SAID ELECTRODE, A PRESSURE RESISTANT SHELL SURROUNDING SAID HEAT EXCHANGE WALL IN SPACED RELATION THEREWITH AND DEFINING A PRESSURE ENCLOSURE THEREAROUND, A BODY OF VAPORIZABLE FLUID IN SAID ENCLOSURE, HEAT DISSIPATING FORMATIONS PROVIDED ON THE OUTER SURFACE OF SAID HEAT EXCHANGE WALL PROJECTING INTO SAID FLUID TO VAPORIZE SAME AND DIMENSIONED IN ACCORDANCE WITH THE RELATIONS B=M$AC AND D<B/3, WHEREIN B IS THE DEPTH OF THE GROOVES, D THE WIDTH THEREOF, A THE AVERAGE THICKNESS OF THE RIBS, C THE HEAT CONDUCTIVITY OF SAID WALL MATERIAL AND M A NUMERICAL FACTOR, SAID HEATDISSIPATING FORMATIONS FURTHER HAVING A DEPTH B LESS THAN 12 MM., SO AS TO ESTABLISH STABLE TEMPERATURE GRADIENTS OVER SAID SURFACES, AND MEANS FOR MAINTAINING A PRESCRIBED PRESSURE ON SAID FLUID WITHIN THE ENCLOSURE OF AT LEAST THREE ATMOSPHERES ABOVE NORMAL ATMOSPHERIC PRESSURE. 